Explosive compositions containing expanded ammonium nitrate in crystalline form and method of preparing same

ABSTRACT

An explosive composition containing as an essential ingredient ammonium nitrate in fine crystalline form having a specific surface greater than 500 cm2/g. The ammonium nitrate in this form is obtained by crystallization from an aqueous solution in the presence of a tensio-active agent such as laurylamine acetate.

llnitefi States Potent 72] Inventor Jacques Chatel dle Raguet lDe Brancion Bonlogne sur Seine, France [21 App]. No. 711%,M3

[22] Filed lFelb. 26, 11963 [45] Patented Nov. 9, 19711 [73] Assignee Societe dlllnplosifis ell de llrodults Chimiquw Continuation-impart of application Ser. No. 558,273, June 17, 1966, now abandoned. The portion of the term of the patent subsequent to 0m. 18, 1983, has been tliselalmed.

[54] EXPLOSIIVIE (IOMIPOSII'I'IIONS CONTAINING EXPANDED AMMONHUM NITRATE 1N CRYSTALLIINIE 1F OlllMl AND METHOD OF [PREPARING SAME 23 (Ilaiins, 3 Drawing Figs.

[52] US. 'Cl 149/2, 149/39, 149/43, 149/44, 149/46, 149/60, 149/87, 149/105 Primary Examiner-Carl D. Quarforth Assistant Examiner-Stephen .l. Lechert, Jr. Attorney-Waters, Roditi, Schwartz and Nissen ABSTRACT: An explosive composition containing as an essential ingredient ammonium nitrate in fine crystalline form having a specific surface greater than 500 cm /g. The ammonium nitrate in this form is obtained by crystallization from an aqueous solution in the presence of a tensio-active agent such as laurylamine acetate.

PATENTEDunv a mi SHEET 1 BF 3 F/Go/ Pmmmm 919m SHEET 3 UF 3 FIG. 3

lEXPlLOSlW/IE COMWSHTHONS CONTAINING EXPANDED AMMONIIUM NllTM'll'lE llN CRYSTALLllNlE FORM AND METHOD 01f" PREPARING SAJWE CROSS-RELATED APPLICATION This application is a continuation-impart of my earlier application, ser. No. 558,273 filed June 17, 1966 and now abandoned.

BRIEF SUMMARY OF THE INVENTION The present invention relates to new explosive compositions having an increased sensitivity and power, as well as to their applications in various fields of use.

lt is known that in recent years, there have been used explosive agents constituted by mixtures of ammonium nitrate and combustible substances such as carbon black and fuel oil. However, the mixtures thus obtained lack sensitivity and can-- not be detonated with a conventional detonator except in the presence of a booster charge. In addition the detonation of these compositions may be imperfect and the velocity of detonation may be insufficient.

It has been discovered however that the character of the ammonium nitrate can be modified with resulting increase in its sensitivity to detonation. In particular, it has been found that by special techniques of crystallization of the ammonium nitrate, high degrees of specific surface can be produced leading to substantially more sensitive explosive mixtures containing the ammonium nitrate.

At first, it was thought that the modification of the specific surface of the ammonium nitrate crystals was related to a modification of the crystal form itself. However, X-ray diffraction diagrams, and photomicrographs reveal that the crystalline system is unchanged, whereas the fine physical structure of the crystals is modified. Ordinary ammonium nitrate consists of large transparent crystals having the touch of sand, whereas the nitrate prepared according to the invention consists of an accumulation of large lamellar pieces which are unctuous and fluffy to the touch. This difference in physical structure is unique to the method of preparation and cannot be obtained by a physical treatment which reduces the size of the ordinary particles.

According to the invention, the sensitivity of the explosive composition has been increased in an entirely unexpected manner by utilizing ammonium nitrate with a specific surface greater than 500 cmF/g.

The modification of the physical structure of the ammonium nitrate is achieved by introducing into the crystallization solution, a surface active agent such as laurylamine-acetate.

The applicant has also been able to make the discovery that certain nitrates can, by compression, be brought to appreciably higher densities, for example to values of 1.1 without loss of their qualities, provided that these nitrates have a specific surface greater than 500 cm. /g.

Thus such a nitrate with a large specific surface, of normal commercial purity, that is to say containing less than 4 parts per 1000 of organic material, when it contains less than I percent of combustible bodies, is not sensitive to an ordinary No. 8, 2g commercial detonator, but it has been found sufficient to detonate it with a high powered and sensitive charge (booster) for which it detonates at a high velocity.

The invention comprises an explosive composition comprising as an essential ingredient ammonium nitrate in crystalline form with a specific surface greater than 500 cm. /g., and preferably greater than 1000 emf/g. More particularly, the in vention relates to an explosive composition in which the specific surface of the ammonium nitrate is between 700 and 6000 cmF/g.

. According to one embodiment of the invention, the explosive comprises an explosive charge constituted by such an ammonium nitrate, in pure form, without admixture with other combustible agents, either solid or liquid.

Additionally, a small amount of an inert material, for instance a heavy material such as barium sulfate, may be added, to increase the density.

it will be understood that the explosive agent thus prepared is considerably superoxygenated. It thus releases on decomposition, oxides of nitrogen. This prohibits it use in mines and only permits its use in an enclosed carrier and in the open air. Charges for seismic research can also be made, which only contain ammonium nitrate and an inert body, whether separated or not from the nitrate.

This has the essential advantage that the product is practically free of danger; particularly for use at sea, it provides a high degree of safety for loading on boats which no longer have to carry an explosive but only ammonium nitrate in containers, the detonators being kept. far from the nitrate in another part of the vessel.

According to a second embodiment, the invention provides explosive compositions constituted by a homogeneous mixture of an ammonium nitrate of high specific surface, as defined above, with a combustible substance or fuel.

in fact, although a nitrate of high specific surface of normal commercial purity, i.e. containing less than 4 parts per 1000 of organic materials, is not, as has been stated above, sensitive to the ordinary commercial detonator No. 82g, when it is mixed with a fuel, preferably liquid, in a proportion of up to 20 percent of fuel, it is transformed into an explosive which, while preserving a high degree of safety, is quite comparable to conventional explosives in its other characteristics, i.e. power, sensitivity, and detonation velocity. It is, in particular, sensitive to detonator No 8, and even to No. 6 or to No. 3.

The fuel may be a finely divided organic material, such as cellulose or carbon black or, preferably, a liquid such as a hydrocarbon or mixture of hydrocarbons, or a mixture of solid or liquid fuels. It is especially advantageous to use organic liquids such as fuel oil or diesel oil.

If desired, the explosive composition may be supplemented by the incorporation of various other substances such as calcium silicide or aluminum powder. The composition may contain one or several nitrates in addition to the ammonium nitrate. in particular, a more or less substantial quantity of alkali nitrates may be added, with or without surface active agents.

The mixture which ensures complete combustion with the excess oxygen provided by the ammonium nitrate, is that which has the greatest power. An excess of oxygen risks the production of nitrogen oxides, and excess fuel tends to produce oxides of carbon. The balance mixture is therefore the best, but it is not critical and a superor suboxygenated explosive may be produced as desired.

The grain size of the ammonium nitrate is no longer an essential characteristic and a nitrate in crystalline or granular form may be used, since the important factor is the small size of the physical structure of the crystals.

A further characteristic of the ammonium nitrate of large specific surface is that it may contain up to about l2 percent by weight of water, in the mass of the crystal and it has been found that the best sensitivity is generally obtained when the nitrate contains aboutS percent, by weight, of water.

It is also possible to use as a fuel, dinitrotoluene or a mixture of dinitroand mononitrotoluene. There may then be produced, according to the invention, a plastic or semiplastic explosive, by mixing it in a homogeneous manner with moist ammonium nitrate, having a specific surface greater than 700 crn."/g. with DNT or ONT. The term moist ammonium nitrate" means a nitrate which contains at least 5 percent of water by weight. Generally, for this purpose, there is used nitrate having up to 12 percent, and preferably 4 to 8 percent of water.

There may also be used various adjuvants such as calcium nitrate, guar gum, etc..., to produce an explosive paste without Tolite or other conventional sensitizers.

Finally, the invention provides explosive compositions, as hereinbefore defined, and comprising in addition, a substantial proportion of an inert material.

In fact, the increase in sensitivity of the fuel-nitrate mixtures by the use of a nitrate of large specific surface is such that it is possible, while preserving in the product the desirable qualities of sensitivity to detonation, transmission of detonation, detonation velocity, etc..., to add to the mixture a large amount of an inert material for the purpose of obtaining secondary effects.

The larger the specific surface of the ammonium nitrate, the more it becomes possible to add inert materials while preserving in the mixture a sensitivity and an acceptable detonation transmision coefiicient.

Thus it is posible to add large amounts of barium sulfate, for example, or ground sodium chloride.

These results are particularly valuable since sodium chloride is an excellent flame-quenching substance and there may thus be obtained a flameproof explosive very cheaply.

It will be understood that it is possible to replace the sodium chloride by other known flameproofing agents, such as sodium bicarbonate or salts of oxalic or formic acid, ammonium oxalate, sodium or calcium forrnate, etc.

It will also be understood that the flame safety obtained varies according to the amount of flameproofmg agent and its granulometry.

Using sodium chloride, for example, there may be obtained an explosive layer (P2) or an improved layer (P3).

By sufficiently increasing the moisture content of the nitrate and the amount of fiameproofing agent, there may even be obtained an explosive agent which is not sensitive to shock.

It is then still possible to detonate such explosive agent means of conventional detonators, such as P3, the composition of which is described below.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is an illustration enlarged l times of the crystal structure of unmodified ammonium nitrate with a specific surface of 350 cmF/g.

FIG. 2 is an illustration enlarged 120 times of the crystal structure of ammonium nitrate produced by crystallization in the presence of a surface active agent and having a specific surface of 2,540 cm."'/g., and

FIG. 3 is an illustration enlarged I20 times of the crystal structure of ammonium nitrate produced by crystallization in the presence of a surface active agent and having a specific surface of 3,l40 cmF/g.

DETAILED DESCRIPTION In order that the invention may be more fully understood, several embodiments are described below with reference to nonlimiting examples.

In the examples, the specific surfaces were measured by the Rigden method, i.e. by the relation between the loss of air under a pressure gradient applied across a bed of compressed powdered material, the specific gravity of the solid, the porosity of the bed and the specific surface of the particles composing this bed.

Example I shows a method for the preparation of ammonium nitrate. Example II illustrates the effect of the size of the specific surface of the ammonium nitrate on its sensitivity. Example llI illustrates the efficacy of ammonium nitrate of large specific surface, in the absence of a fuel. Examples IV and V illustrate the compositions formed by the mixture of such a nitrate with a fuel, and examples VI and VII illustrate embodiments wherein inert fillers are added to such compositions.

EXAMPLE I A dripping apparatus is used, which consists of a stainless steel sheet tank on the external wall of which ammonium nitrate solution to be crystallized is caused to drip. Inside the tank, a cooling liquid, which may be water, brine, or any other suitable liquid, is caused to circulate and is pulverized, the temperature of this cooling liquid being adapted to the temperature at which crystallization is achieved, i.e. between l4 and 33 C.

The mixture of crystals and mother liquor is withdrawn at the lower part of the tank and is collected on a conveyor belt,

in order to be conveyed to a separator (decantation apparatus, filter, or drier).

With this apparatus, an aqueous nitrate solution, having a concentration corresponding to the saturation at 33 C. and containing, according to the test, different concentrations of a modifying agent, and, in the present case, laurylamine acetate, is subjected to crystallization at 25 C.

A visual and tactile examination of samples of results ammonium nitrate reveals the completely different structure which results from the presence of the laurylamine acetate during crystallization, whereas from examinations of X-ray diffraction patterns, the crystalline system remains orthorhombic for all the samples although clearly less defined as seen in FIGS. 2 and 3. In fact, up to the present time, no satisfactory explanation of this fact could be found. It may be noted that, to these differences in the physical structure, correspond outstanding difi'erences (about l0 times greater for the nitrate of FIGS. 2 and 3 than for FIG. I) of the specific surfaces, and that nitrates which have this high degree of specific surface have themselves, the property leading to much more sensitive explosive mixtures than the nitrate with the smaller specific surface (i.e. below 500 cm.*/g.).

EXAMPLE II In order to evaluate the effect of the large specific surface of the ammonium nitrate according to the invention, the sensitivity of ammonium nitrate was evaluated for varying values of specific surface thereof as obtained by the method of example I. The results are listed in the table given hereinbelow wherein the sensitivity (or self excitation coefficient) is measured by the distance in centimeters at which an emitting car tridge primes a receiving cartridge disposed in a straight line in sand. The cartridges were paper and had a diameter of 30 mm. and contained 95.5 percent ammonium nitrate, 4.5 percent fuel, with general water content varying from 0.5 to 4 percent.

Specific Surface in Total number of Average sensiti- A striking fact appears from the attached table. Thus, whereas one might logically expect that the properties of the nitrate vary in a continuous manner as a function of the variations of its specific surface, it appears that in the first three measurements, the sensitivity of the system used is null, and then suddenly varies from about 700 cm.'-/g. onward and substantially increases.

EXAMPLE Ill A cylindrical container 130 mm. diameter and 480 mm. long of tinned iron, is filled with ammonium nitrate of 1,600 cmF/g. specific surface at 1 percent humidity. There is thus obtained a charge density of 0.9.

This charge contains neither organic fuel nor oxidizable metal (such as aliminum or magnesium) and is detonated by a booster Pentolite of 20 f. It detonates with great violence.

The complete detonation of such a charge is obtained with a booster of 2.5 g. of Pentolite detonated by a NO. 8 commercial detonator.

EXAMPLE IV Various explosive compositions were prepared by homogeneously mixing together ammonium nitrate of various specific surfaces and 4 percent by weight of diesel oil. Each of the resulting compositions was introduced into paper cartridges so as to give a filled cartridge of 100 g. weight, 30 mm. diameter and 0.9 g./cc. apparent density.

The cartridges were then detonated with a No. 6 commercial detonator.

The following table shows the relation between the explosive properties of each respective explosive composition and the specific surface of the ammonium nitrate employed 1' by weight Ammonium nitrate (s ecific 88.0

surface 3000 cmlg Dinitrotoluene 8.5 Orlhonitrotolucnc 3.5

The ammonium nitrate had a :moisture content of about 6 percent by weight.

This explosive is plastic at normal room temperatures and has a density of 1.1 g./cc. It is detonated by a No. 8 detonator in cartridges of mm. diameter, and gives a gap test of5 cm. A pierced paper cartridge of this composition has been detonated after being immersed for half an hour in water.

The plastic explosive compositions of the invention may contain, if desired, waterproofing agents of the type commonly employed in the production of water-resisting explosives. For example, the composition described in the foregoing example Vll may have incorporated therein 0.5 percent by weight of calcium stearate and 0.5 percent by weight of sodium carboxymethylcellulose as protecting agents.

The following table illustrates the properties of a certain number of other compositions all including a solid fuel, with a nitrate of high specific surface, itself with or without a liquid f l. therein. ue

Coalficlvnt Detonof ated sunslveloc- Solld fuel tlvlty it Nitrate (percent) percent (cm in. s Power Composition No I 1 80(Wltl12Z,Wnttl).. SlCn-Zt) l 600 2, J5 (4% fuel Oil) SlCn-fi 6 5,000 114 SiC '.Z.l' t 3.. 9s L i l t 4.200 123 4.. .l5. Al-fi ti 3,200 124 5... 97.5 (2% fuel) Fr 'ro-Si-2,5 5 3,250 116 Al-5 Fprrwsps I (I 2,800 135 7 86 Cellulose-l4 3 2,900

Cellulose-7 l It has been found that when the specific surface of the ammonium nitrate is of the order of 1,700 cm. /g., complete 55 detonation can be obtained using paper cartridges of 25 mm. diameter. Even when unconfined such a composition can be detonated with a No. 3 detonator. With a commercial No. 8 detonator and unconfined paper cartridges, complete detonation can be obtained with diameters of 15 mm. and even less. However for the smaller diameters the cartridges need to be in contact with the detonator for the detonation to be transmitted.

Another advantage of using ammonium nitrate of high specific surface is that with a normal packing density of about 0.8 g./cc. it is possible to compress it in cartridges of 30 mm. diameter without substantial loss of its good properties. Compressed to a density of 1.06 g./cc. the ammonium nitrate composition can maintain a sensitivity of 4 cm. with a No. 8 detonator.

EXAMPLE V A plastic explosive composition was prepared from the following:

The nitrates of composition Nos. 1 to 4 had a specific surface of 1200 cmF/g: those of compositions 5-6 of 2000 cmF/g. and those ofcompositions 7-8, of 1800 cm.*/g.

Firing tests were conducted in paper cartridges of 30 mm. diameter, detonated by No. 8 2 g commercial detonators.

EXAMPLE. Vl

If there is added to a mixture of 96 percent of ammonium nitrate of specific surface 2000 cmF/g. and of4 percent of fuel oil an increasing percentage of ground BaSO the following results are obtained:

It is seen that it is possible to increase the density of the explosive and to improve its sensitivity and its detonation velocity by adding a small amount of barium sulfate.

EXAMPLE Vll If in place of barium sulfate there is substituted ground sodium chloride, the results shown in the following table are obtained:

The oxygen balance can still be adjusted with cellulose and the following formulation was prepared:

ammonium nitrate 65.8 fuel oil 2.8 NaCl 29.4 cellulose 2 ammonium nitrate 71 diesel oil 4 NaCl (fine) 25 has a power of 0.69 relative to picric acid and gives a flame safety in angle mortar fire appreciably equal to that of the explosive of the same power which has the composition:

nitroglycerine ammonium nitrate (ordinary) sodium chloride 28 cellulose 5.5 kaolin 0.5

calcium stearate l and which is classed in England among Permitted P3" explosives, i.e. EQS, which corresponds in France to the categorie amelioree PQS-P3.

As additional properties of this novel nitrate, it may be noted that whereas in the previous nitrates it was possible, if necessary, to crush the crystals in order to obtain specific surfaces of about 600 cm. it is, on the contrary, impossible, by means of a further compression, to exceed a density of 0.85. In the present case, on the contrary, the nitrate may be compressed until a density of 1.05-l.1 is obtained, while maintaining its good explosive qualities.

It is also possible, with the nitrate of the invention, to proceed with the following operations, which are absolutely impossible to perform with ordinary nitrates:

This new nitrate perfectly explodes with a density of about 1, and with a detonation speed of 3,500 m./sec., with cartridges having a 30 mm. diameter.

The mixture prepared with a 7 percent water content still explodes when primed with cartridges of a 20 mm. diameter, which is impossible with ordinary nitrate, even dry.

With a 7 percent water content, the same mixture has a 3 cm. sensitivity with 30 mm. diameter cartridges.

1t is possible to incorporate in this new nitrate inert materials, and even cooling salts such as sodium chloride; a mixture of nitrate according to the invention with fuel and 30 percent sodium chloride explodes in 30 mm. diameter cartridges.

With the nitrate according to the invention with 5 percent water, products with semigelatinous consistency having the following compositions may be prepared:

F lrst composition:

ammonium nitrate with a specific surface of 800 cm."/g. 89

percent ortho-nitro-toluene: 3 percent di-nitro-toluene: 8 percent Second composition:

nitrate: 86.5 percent glycol: 13.5 percent These two compositions have a density of 1.05 and a 3 cm. sensitivity in 30 mm. diameter cartridges.

The above properties are very striking when compared to the data Chemistry and Technology of Explosives" of Urbanski, pages 482, 483. in which is indicated that the minimum diameter in steel tube with 4.5 percent diesel oil and 0 percent water is about 30 mm., provided priming is made by a No. 8 detonator reinforced with 27 g. compressed TNT. For 5 percent water, the detonation is obtained, always with steel tube, with the same reinforced priming, in 37 mm. diameter. With the nitrate of the Application, cartridges are paper cartridges and No. 8 detonators currently sold, without reinforcing means. The same paper cartridges of 30 mm. diameter an containing 95.5 nitrate and 4.5 diesel oil are also sensitive to detonator No. 3, i.e., containing 0.54 g. fulminate-chlorate.

What is claimed is:

1. An explosive consisting essentially of expanded ammonium nitrate in a crystalline form said expanded ammonium nitrate having a specific surface area greater than 500 cm./g. and a density of at least 0.85 in combination with a fuel selected from the group consisting of carbonaceous fuels, noncarbonaceous fuels, and mixtures thereof.

2. An explosive composition according to claim 1, wherein said specific surface is greater than 1000 cmF/g.

3. An explosive composition according to claim I, wherein said specific surface is between 700 and 6000 cm."'/g.

4. An explosive composition according to claim 1, wherein the density is between 1.05 and 1.10.

5. An explosive composition according to claim 1, wherein said fuel is present in a proportion between 1 and 20 percent by weight.

6. An explosive composition according to claim 1, wherein said fuel is present in a stoichiometric amount.

7. An explosive composition according to claim 1, wherein said fuel is a powdered solid.

8. An explosive composition according to claim 9, wherein said powdered solid is carbon black, cellulose, a metallic powder or sodium silicide.

9. An explosive composition according to claim 1. wherein said metallic powder is aluminum.

10. An explosive composition according to claim 1, wherein said fuel is a liquid.

11. An explosive composition according to claim 12, wherein said liquid is a hydrocarbon or a mixture of hydrocarbons, diesel oil, mononitrotoluene or dinitrotoluene.

12. An explosive composition according to claim 1, containing up to 12 percent water.

13. An explosive composition according to claim 14, wherein the water is present in an amount from 4 to 8 percent water.

14. An explosive in water resistant according to claim 1.

15. An explosive composition according to claim 1 in paste form.

16. An explosive composition according to claim 1, including an inert material.

17. An explosive composition according to claim 20, wherein said inert material is barium sulfate.

18. An explosive composition according to claim 20, wherein said inert material is a flameproofing substance.

19. An explosive composition according to claim 22, wherein said flameproofing substance is sodium chloride, sodium bicarbonate, an oxalate or a formate.

20. An explosive composition according to claim 1 including less than 4 percent of fuel.

21. An explosive composition according to claim 1, including less than 1 percent of fuel.

22. A method of producing an explosive composition comprising forming an aqueous solution of ammonium nitrate containing a surface active agent, crystallizing the ammonium nitrate in the presence of said agent at a temperature of between -14 and 33 C. and thereafter mixing said ammonium nitrate with a fuel selected from the group consisting of carbonaceous fuels, noncarbonaceous fuels, and mixtures thereof.

23. A method according to claim 22 wherein the surface active agent is laurylamine acetate.

plastic form composition 

2. An explosive composition according to claim 1, wherein said specific surface is greater than 1000 cm.2/g.
 3. An explosive coMposition according to claim 1, wherein said specific surface is between 700 and 6000 cm.2/g.
 4. An explosive composition according to claim 1, wherein the density is between 1.05 and 1.10.
 5. An explosive composition according to claim 1, wherein said fuel is present in a proportion between 1 and 20 percent by weight.
 6. An explosive composition according to claim 1, wherein said fuel is present in a stoichiometric amount.
 7. An explosive composition according to claim 1, wherein said fuel is a powdered solid.
 8. An explosive composition according to claim 9, wherein said powdered solid is carbon black, cellulose, a metallic powder or sodium silicide.
 9. An explosive composition according to claim 1, wherein said metallic powder is aluminum.
 10. An explosive composition according to claim 1, wherein said fuel is a liquid.
 11. An explosive composition according to claim 12, wherein said liquid is a hydrocarbon or a mixture of hydrocarbons, diesel oil, mononitrotoluene or dinitrotoluene.
 12. An explosive composition according to claim 1, containing up to 12 percent water.
 13. An explosive composition according to claim 14, wherein the water is present in an amount from 4 to 8 percent water.
 14. An explosive in water resistant plastic form composition according to claim
 1. 15. An explosive composition according to claim 1 in paste form.
 16. An explosive composition according to claim 1, including an inert material.
 17. An explosive composition according to claim 20, wherein said inert material is barium sulfate.
 18. An explosive composition according to claim 20, wherein said inert material is a flameproofing substance.
 19. An explosive composition according to claim 22, wherein said flameproofing substance is sodium chloride, sodium bicarbonate, an oxalate or a formate.
 20. An explosive composition according to claim 1 including less than 4 percent of fuel.
 21. An explosive composition according to claim 1, including less than 1 percent of fuel.
 22. A method of producing an explosive composition comprising forming an aqueous solution of ammonium nitrate containing a surface active agent, crystallizing the ammonium nitrate in the presence of said agent at a temperature of between -14 and 33* C. and thereafter mixing said ammonium nitrate with a fuel selected from the group consisting of carbonaceous fuels, noncarbonaceous fuels, and mixtures thereof.
 23. A method according to claim 22 wherein the surface active agent is laurylamine acetate. 